The Sedimentary Context of Dinosaur Fossils Dinosaur fossils are found in sedimentary rocks
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The Sedimentary Context of Dinosaur Fossils Where do paleontologists find dinosaur fossils? Dinosaur fossils are found in sedimentary rocks Sedimentary rocks preserve information vital to understanding dinosaurs Environment of deposition Physical habitat where dinosaur lived Ecological habitat - plants / other animals Taphonomic (“death”) circumstances Circumstances of demise How did the fossil become preserved? Depositional Environments Environments where dinosaurs lived Environments where dinosaurs did not live Upland Forest Reef Floodplain Shelf Desert Deep Ocean Coastline Dinosaur fossils commonly found Dinosaur fossils usually rare Floodplain Upland Forest Coastline Shelf Desert Dinosaur fossils absent Reef Deep Ocean Active sedimentary deposition Floodplain Coastline Desert Rare sedimentary deposition Upland Forest We know a lot about dinosaurs that lived in active depositional environments. Shelf Tectonics - movement of the Earth’s crust Preserving fossils requires two things: A: Lots of sediments B: Some place to deposit them (a depression) Most places on Earth at any given time are NOT sites of sediment deposition, rather, they are sites of erosion. No fossils preserved! Most sediment ends up being carried by rivers and deposited offshore on the continental shelf. Few dinosaurs preserved! Tectonics - movement of the Earth’s crust Trapping sediments in continental environments requires active subsidence (downward movement) of the crust. Subsidence is usually related to major tectonic events that disturb the crust. A: Orogeny (mountain building) related to plate collisions. B: Rifting (plate separation) Andes Mts. African Rift Valley Erosional Foreland deposition deposition Andes Mountains and Amazon Basin Nevadan Orogeny Late Jurassic Alluvial plain (Morrison Formation) Colliding volcanic arc Rising Mountains Dinosaur-bearing rock formations Laramide Orogeny Sevier Orogeny Nevadan Orogeny Poor record of Early and Middle Jurassic Dinosaurs Sonoma Orogeny West Coast Mountain-Building Episodes (Orogenies) During the Mesozoic Era. Morrison Formation, Vernal, Utah Dinosaur National Monument, Vernal, Utah River channel sand bar environment Morrison Formation Morrison, Colorado river channel floodplain Dinosaur trackways Morrison, Colorado Dinosaur bone Morrison, Colorado Dinosaur bone Morrison, Colorado Sevier Orogeny Cretaceous Alluvial plain (Dakota Sandstone) Subducting Seafloor Uplifted Mountains Interior (epicontinental) seaway Wave ripples Wave ripples and trace fossils Mangrove root traces Iguanodont trackways Dakota Sandstone Early Cretaceous Iguanodont trakways Mesozoic Rock Formations in the NY Region Mesozoic rock formations in the NY region Early Jurassic Late Triassic Late Cretaceous Geologic Provinces NY Region Timescale and geologic provinces of NY-NJ Breakup of Pangea - Late Triassic Onward Breakup of Pangea Source: Dietmar Muller - Sydney University. Rifting tectonics Schlische, R.W., and Withjack, M.O., 2001, Styles of secondary faulting and folding associated with oblique deformation: AAPG Annual Meeting Abstract, v. 10, p. A179. Mesozoic rift basins in North America Source: http://geology.rutgers.edu/103web/Newarkbasin/NB_geology.html Half-Graben Rift Basin Half-graben rift basin Schlische, R.W., 1994, Rifting in eastern North America: Virginia Explorer, v. 10, p. 20-23. Geologic Map of the Newark Basin Geologic map of the Newark Basin Cro Sec ss tion Source: http://geology.rutgers.edu/103web/Newarkbasin/NB_geology.html Modified from Schlische (1992) and Olsen et al. (1996). Geologic cross section of the Newark Basin Sedimentary deposition in a growing rift basin Lake and shoreline beige siltstone and dark shale Braided river / floodplain red sandstone and siltstone East Alluvial fan conglomerate and arkose West Bounding fault Sedimentary deposition in a growing rift basin Alluvial fan conglomerate and arkose East West Bounding fault Stockton Formation alluvial fan conglomerates Sedimentary deposition in a growing rift basin Braided river / floodplain red sandstone and siltstone East West Bounding fault Stockton Formation - conglomerate and arkose River channel and floodplain deposits, New Haven Arkose Ancient soil horizon (caliche) in New Haven Arkose Sedimentary deposition in a growing rift basin Lake and shoreline beige siltstone and dark shale East West Bounding fault Dinosaur footprint and ripple marks in sandstone (DSP, Hartford basin) Lockatong Formation - shale and siltstone deposited in a rift lake Semionotus - Triassic freshwater fish Floodplain to lake sediment cycle, New Berlin, CT flo o dp lain Lak e sh ore De ep La lak ke e flo sho od re pla in Theropod trackways, Dinosaur State Park, CT Mesozoic Rock Formations in the NY Region Mesozoic Rock Formations in the NY Region Late Cretaceous Late Cretaceous Middle - Late Cretaceous paleogeography Zuni Sea Atlantic shoreline far inland of present position Geologic map of the Atlantic Coastal Plain Upper Cretaceous Navesink Formation, Big Brook, NJ Common Navesink Formation Fossils Oysters Brachiopod Choristothyris plicata Pycnodonte mutabilis Exogyra costata Cephalopod Belemnitella americana Agerostrea mesenterica Upper Cretaceous dinosaurs of NJ Upper Cretaceous Dinosaurs of NJ Hornerstown Sand Tinton Sand G G G G G G G G G G G G G G Red Bank Sand Navesink Fm. Cycle 3 G G G G G G G G G G Mount Laural Sand Cre ta ce ou s Maastrichtian Campanian Cycle 2 Wenonah Fm. Marshalltown Fm. Tertiary Cretaceous Meters 0 Feet 0 20 G G G G G G 10 20 Englishtown Fm. 40 60 80 Key Gravel Woodbury Clay Cycle 1 Sand Hadrosaurus foulkii Nodosaurid ankylosaur Dryptosaurus (Tyrannosaur?) Ornithomimosaur (Coelosaurus) Hadrosaurs (Hadrosaurus spp.) G Merchantville Fm. G G G G Silt - Mud G G G G G G G G G G G G G G G G G G G G Glauconite G Figure 1. Upper Cretaceous Stratigraphy of the New Jersey Coastal Plain 2 Taphonomy and Depositional Environments The Flaming Cliffs Ankylosaur Excavation Oviraptor excavation Oviraptor skull and egg Protoceratops adult and juvenile Lizard Fossil Mammals Deltatheridium Zambdelestes “Fighting Dinosaurs” Velociraptor Protoceratops Ukhaa Tolgod Facies E1: cross-bedded sands with dinosaur footprints, but no skeletons. E2: massive sands with inclined caliche nodules, no skeletons. F: massive sands, structureless, with perfectly preserved vertebrate skeletons. Interpretation: deposition by actively migrating sand dunes. E1 Facies Dinosaur footprint in beds of E1 facies. Dinosaur footprint in beds of E1 facies. Interpretation: dune failure and slumping, massive sand flows. F Facies Interpretation: stabilized dune deposits trampled by dinosaurs. E1 Facies E2 Facies Sand Hills, Nebraska vegetated sand dunes Dinosaur footprint at Ukhaa Tolgad Bison footprint in Sand Hills dune Large scale slumping on the slope of a dune, northern Mexico Sand Hills, Nebraska Excessive rainfall can cause dune front to fail and sand to flow rapidly downslope, burying landscape beneath structureless alluvial fan deposits. Animals preserved at Ukhaa Tolgod were buried alive in massive, fluidized sand avalanches.
